2018

£30m

Contact

Services we provided

Reopened in May 2018 by David Attenborough, Temperate House is a magnificent Victorian glasshouse in the heart of Kew Gardens. A five year restoration project has repaired and updated the building ready for today's visitors and tomorrow’s needs.

The Royal Botanic Gardens (RBG) at Kew is a magnificent 300 acre parkland site on the western fringes of London. The site has been home to rare, exotic and beautiful flora from around the world since the mid-18th Century, and in 1840 the gardens were permanently opened to the public as a national botanical garden. Recognised globally for its importance in the promotion of botanic studies and the preservation of endangered species, in 2003 is was designated a UNESCO world heritage site.

A number of botanical glasshouses display the more delicate plants in favourable conditions. The largest of these, Temperate House, designed by architect, Decimus Burton, was first opened in 1863, although it took a further 33 years to complete. Rising to 18 meters and with over 15,000 panes of glass it's now the largest surviving Victorian glasshouse in the world. For over 150 years Temperate House has been home to temperate plants from Africa, Australia, New Zealand, the Americas, Asia and the Pacific Islands. It allows the visiting public to admire 10,000 plants from 1,500 rare and wonderful species close up, while playing a vital role in preserving species for research.

Despite previous restoration projects, most recently in 1980, weathering had taken its toll on this Grade I listed building, and it was in need of fundamental repair. With funds raised by public appeal, a £15m heritage lottery donation and an additional grant from the Department of Environment, Food and Rural Affairs (Defra), the path was cleared to not only restore Temperate House to its former glory but update and improve the facility for the benefit of future generations.

Ramboll was appointed lead consultant and conservation engineer for the refurbishment in 2013. An initial survey conducted by the incumbent engineer had revealed considerable corrosion and decay. This was most apparent in the extensive wrought iron, cast-iron and steelwork comprising the structural frame. The paint systems had failed widely, window mechanisms broken and the glass itself etched with dirt and deposits.

Project detail

Initially it had been proposed to dismantle, repair and rebuild the entire structure, but this would have been prohibitively expensive. Ramboll proposed a more cost-effective solution, requiring the removal of the glazing system only, so that work to the structural frame could be performed from scaffolding with minimal deconstruction. Ramboll developed the schedule of repair by a regime of prompt inspection of the metalwork in the period between the existing coatings being removed and the new system being applied. The majority or repairs were successfully undertaken insitu and dismantling successfully kept to a minimum.

Assessing, restoring and repairing

As newly appointed lead engineering consultant Ramboll produced the initial condition report, identifying corrosion from failure of existing paint systems to metalwork as the primary defect. Close inspection by engineers on mobile elevating work platforms (MEWPs) revealed the full extent of the damage to the ironwork.

The detailed report allowed for the creation of a schedule of necessary repair works, planning contingency for change once the existing paintwork was removed from the structural frame.

Centre block high-level walkway plates were in a severely corroded state and had to be disposed of and replaced. The main reason was that water had got into the interfaces with supporting steelwork. We overcame a repeat of this by offsite painting of new plates and using a rubber bearing on top of the site-painted support structure.

To facilitate the repair of the frame, the 1980s aluminium-framed glazing system had to be removed, refurbished and stored until it could be reinstated. To ensure fit during the reinstatement every element was given a unique ID, scheduled with its location and double-tagged.

Two key objectives of the project were to improve daylight and ventilation available to the specimens. We discovered that the condition of the old glass was such that its transparency could not be restored to acceptable levels. The glass needed to be replaced throughout, with the old glass sent for recycling. The opening lights used to ventilate the building and prevent overheating were restored to operation. We designed solutions for providing more control over the heating and ventilators, with the key lights now controlled via the new building management system.

With maximising public access a critical objective, we conducted a review of the architect's and MEP engineer's layouts for improving access throughout the glasshouse, for RBG staff. The Ramboll team identified further work necessary to deliver on the original plans. This included reinforcing concrete services trenches below the pathways in the central block, and altering the basement layouts in the north and south octagons.

Conserving, preserving and protecting

While most plants were relocated to alternative glasshouses for the duration of the works, seven of the rarer species of tree were either too large or too sensitive to relocate. Kew took cuttings as a back-up and the trees were wrapped in a suitable enclosed covering and provided with their own lighting and heating. RBG staff inspected and watered them regularly throughout the four years of the project. Two of the trees survived this environment, one each in the North Block and South Block; however, we were not so lucky with the remainder, which had to be replaced from specimens grown from the cuttings.

With all parties in agreement on the detailed plans the repair operation could begin in earnest. Inevitably with any major project unforeseen issues arise. External below-ground services were challenged by uncertainty with the record information over many, many years of development and alteration. As the contractors began on their excavation works they uncovered old brick pathways, a well and Victorian heating pipes dating back to the original Decimus Burton construction. With our resident engineer on site and the backing of Ramboll's Heritage and Archaeology team we ensured everything of historical interest, was retained and built-in where possible, or recorded and safely removed. This included Victorian 116 urns and statues. In total, over 69,000 individual elements were removed from the building and cleaned, repaired or replaced.

Ensuring quality

Absolutely vital to the success of the project was the restoration of metalwork. Contractors used ultra-high pressure (UHP) water to strip successive layers of paint from the metalwork. With the metal exposed our experts could conduct an element by element inspection, allowing the identification of further defects.

Some of the defects we uncovered at this stage included cracks, breaks, delamination, casting and rolling defects, corrosion between poor fitting surfaces, broken or missing bolts and missing elements. With contractors working to a tight schedule it was crucial that inspections took place as and when the metalwork was exposed, requiring comprehensive record keeping and the fast production of sketches and scheduling of repairs.

With the all the defects exposed and understood we were able to schedule all necessary metalwork repairs for the contractor to undertake, followed by close inspection of the repair work undertaken. This required monitoring and inspections of flash blast and application of three-coat paint system (including film thickness checks).

Buildings of his age inevitably bring issues of level and dimensional discrepancy, and adjustments required to aspects of the site design (for example the site design of trench covers needed to be much slimmer after services were installed too high). The final tasks involved checking the general quality of structural work against specifications, and overseeing and inspecting snagging, ready for the grand opening.